【Domestic Papers】Defect formation and modification of optical properties in β-Ga₂O₃ via carbon ion irradiation

      Researchers from the Qufu Normal University have published a dissertation titled "Defect formation and modification of optical properties in β-Ga₂O₃ via carbon ion irradiation" in Optics Express.

Project Support

      This research supported by National Natural Science Foundation of China (12205167); China Postdoctoral Science Foundation (2024M761751) and Natural Science Foundation of Shandong Province (ZR2023LLZ015, ZR2024LLZ012).

Background

      As an ultra-wide bandgap semiconductor material, gallium oxide (Ga₂O₃) exists in five polycrystalline variants: α, β, γ, δ and ε. Among these, β-Ga₂O₃ exhibits superior thermodynamic stability and belongs to the monoclinic crystal system (space group C2/m). Its tructure comprises GaO₄ tetrahedrons and GaO₆ octahedrons. This material possesses a bandgap of 4.8 eV, with its absorption edge located in the solar-blind region (<280 nm). It also demonstrates high stability against intense electric fields and chemical corrosion, making it promising for applications in MOSFETs, saturable absorbers, solar-blind detectors, Schottky barrier diodes, transparent conductive electrodes, and photovoltaic cells.

Abstract

      Precisely regulating the optical properties of β-Ga₂O₃ crystals is critical for advancing optoelectronic devices such as solar-blind detectors, optical modulators, and Schottky barrier diodes. This study employed 15 MeV carbon (C) ions to irradiate β-Ga₂O₃, revealing lattice defect aggregation at a depth of 6 ∼ 7 µm, accompanied by increased surface root-mean-square roughness, compressive strain-induced lattice distortion, and elevated oxygen vacancy concentration. Irradiation-induced defects act as non-radiative recombination centers, suppressing photoluminescence (PL) intensity. Additionally, these defects contribute to reduced ultraviolet (UV) absorption and bandgap narrowing in β-Ga₂O₃. This work demonstrates the profound impact of C-ion irradiation on the optical properties of β-Ga₂O₃, offering insights into ion beam engineering for ultra-wide bandgap semiconductor optimization.

Conclusions

      In summary, this work systematically investigates the effects of 15-MeV C-ion irradiation on the microstructure and optical properties of β-Ga₂O₃ single crystals. SRIM simulations, combined with optical microscopy observations, reveal that irradiation at this energy induces structural modifications within a depth of 6 ∼ 7 µm in β-Ga₂O₃. AFM analysis reveals a 208% increase in surface root-mean-square roughness (Rq from 0.271 nm to 0.837 nm) post-irradiation. XRD, Raman spectroscopy, and XPS analyses indicate shortened bond lengths and a significant elevation in V_O concentration in the irradiated β-Ga₂O₃. In terms of optical characteristics, significant quenching of the PL intensity is observed, which is attributed to the increased concentration of non-radiative recombination centers (e.g., V_O and V_Ga + V_O complexes) introduced by ion irradiation. Additionally, the ultraviolet absorption spectra exhibit reduced intensity accompanied by a 0.13 eV narrowing of the bandgap, demonstrating defect-mediated modulation of light absorption properties. These quantifiable changes validate the effectiveness of carbon ion irradiation in engineering the optical behavior of β-Ga₂O₃.